Can't access router, VOIP, limited connectivity

Thanks in advance for any help provided. I am absolutely pulling my hair out over this.

I will start with my set up:

Scientific Atlanta Cable modem (2200 M/N?) ---> Linksys SPA-2102 VOIP ---> Netgear 3500L Wireless Router (Stock firmware, unable to upgrade to DD-WRT). This is also my preferred set up as I want to keep the VIOP in front of the router.

The router is given a static IP address by the VOIP unit of 172.16.0.2

Upon power cycling the router, I am able to access the administration page at 192.168.1.1 or routerlogin.net. After a period of 10 - 30 minutes, I receive a limited or no connectivity pop up on XP. I am still able to access the internet without a problem, however I cannot access the routers administration page until I power cycle.

During the 10 - 30 minute period all of my IP addresses assigned my the router show up as 192.168.1.XXX, after the limited or no connectivity message the addresses are changed to 172.16.0.XXX. This really plays games with my port forwarding that is set up. I am still unable to access the routers administration page. I have had luck once in awhile accessing it at 172.16.0.2.

I do get a warning on the routers administration page after a reset that the IP address of the router has been changed to 192.168.1.1 to avoid a conflict.

I have reset all settings of the VOIP and router to factory many times and still I have no luck.

Thanks for taking the time to read this long post, but I wanted to provide as much information as possible.

Your VoIP Device should be within your router not in front of it.

It should be like this:

Modem > Router > All your Internet Connected Devices

Thanks CryptoDan, however although this setup is new (about one month), my previous router a Netgear WNR834bv2 w/ DD-WRT was set up in the exact same configuration and I have had no issues with that set up.

The SPA-2102 is a router although it only has one ethernet port. My set up is like this because I require my VOIP traffic to take all priority and I am simply out of ports on the back of the router.

You should be able to login to your VoIP Providers My Account service, and set up the bandwidth required. I have Lingo, and currently have it set to Max which is 90kilobits a second. Check with your VoIP Service needs.

Not sure if this was directed at me or not. I think you may have meant this for another topic.

I am willing to try anything, but I know this is not the problem.

Basically the only thing different from my past set up is the new router with all default settings.

Well right now your VoIP Device is acting as the DHCP Server so you need to fix that, and by doing so you will have to put the router between your modem and internal connections.

Yes that comment I made was directed to you.